The present invention relates to an electromagnet for a hydraulic system according to the preamble of claim 1.
An electromagnet is used, for example, for a holding device or an electromagnetic valve. This electromagnetic valve may, for example, operate as a pressure control valve, pilot valve, volume control valve, or switch valve in the hydraulic system of an automatic transmission of a motor vehicle in order to, for example, control transmission components, such as clutches or actuators to engage gears.
From DE 41 33 536 A1 a generic electromagnetic valve is known that comprises an armature chamber that is filled with hydraulic medium, that can be fluidically connected to a hydraulic line, and in which an armature is mounted such that its stroke is adjustable. The hydraulic medium contained in the armature chamber is used for cooling, lubricating, and hydraulically damping the armature. The armature interacts with an electrically controllable coil part of the electromagnetic valve, said coil part being provided outside the armature chamber. The armature comprises a shut-off body, by means of which at least one flow opening of a hydraulic line can be controlled. The shut-off body of the armature presses against a return spring so that the electromagnet works against the restoring force of the return spring during a stroke movement of the armature.
The armature furthermore divides the armature chamber into a chamber facing the flow opening (hereinafter referred to as opening-side chamber) and an inner chamber facing away from it. During a stroke movement of the armature adjustably mounted in the armature chamber of the electromagnetic valve, an oil exchange occurs between the opening-side chamber and the inner chamber, during which exchange the hydraulic medium can overflow from the opening-side chamber into the inner chamber for the purpose of volume and pressure compensation. The oil exchange (displacement suction) occurs during stroke movements of the armature, when the displacement volume in the inner chamber and in the opening-side chamber of the electromagnetic valve is different.
In a common electromagnetic valve used in motor vehicle transmissions, the oil exchange between the inner chamber and/or the opening-side chamber of the electromagnetic valve and the surroundings generally occurs using an oil pan. In doing so, the following problem exists: For example, the oil exchange occurs directly to the oil pan, which can contain metal particles in particular as a result of the abrasion of the gear set or the clutches. The hydraulic medium (hereinafter referred to as hydraulic oil) is therefore contaminated with magnetic particles, which can be attracted by the electromagnet. During an oil exchange, the particles can find their way into the armature chamber of the electromagnetic valve and cause undesirable functional impairments there, such as a disturbance of the magnetic field, a clogging of the movement corridor of the armature as well as a change of the tribological system between the armature and the inner wall delimiting the armature chamber. The particles furthermore generally remain in the armature chamber since magnetic fields prevail here due to residual magnetization or due to the electromagnet, which magnetic fields prevent flushing. In addition, dirt can be sealed off in the inner chamber via a small armature gap between the armature and the inner circumferential wall delimiting the armature chamber.
In order to increase the degree of purity of the hydraulic oil, filters are used in common hydraulic systems. The filters reduce the number of particles in the hydraulic system.
From DE 2011 055 093 A1 is known an electromagnetic valve, in which a receiving chamber is arranged fluidically upstream of the opening-side chamber of the armature chamber. In the receiving chamber is provided a floating disk, which reduces the dirt ingress of contaminating particles into the inner chamber of the armature chamber of the electromagnetic valve.